Midblock sulfonated styrenic block copolymers are known. Typically, they are sulfonated block copolymers based on styrene and/or t-butyl styrene with the former predominantly used in a midblock, that is subsequently sulfonated and the latter in the endblocks, that resist sulfonation. These polymers are in a solid state in the presence of water and have both high water transport properties and sufficient wet strength. These polymers are known to have excellent barrier properties.
From WO Pat. No. 2007010039 a midblock sulfonated styrenic block copolymer is known. This block copolymer is based on a block copolymer that comprises at least two polymer end blocks A and at least one polymer interior block B wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation, and wherein said A and B blocks do not contain any significant levels of olefinic unsaturation.
Such polymers are now commercially available for instance under the trademark Nexar® from Kraton Polymers. The typical structure of a Nexar molecule is a pentablock consisting of two poly(t-butylstyrene) (tBS) blocks, two poly(ethylene/propylene) (EP) blocks (hydrogenated polyisoprene), and in the middle a partly sulfonated polystyrene (sPS) block.
Such midblock sulfonated block copolymers are typically delivered to customers as a solution of about 10% in a combination of heptane and cyclohexane. For some customers this poses a problem because they are not used to handling this type of solvent and do not have adequate ventilation and disposal systems in place. Organic solvent may cause various handling problems due to the high volatility and low flame point of such solvents. The possibility to deliver such polymers as an aqueous emulsion would be a solution. Moreover, a waterborne system is more environmental friendly. Preparing a suitable aqueous emulsion, however, is not without its own problems.
Because of its excellent water transport properties, these polymers may be used in textile coatings. When used in textile coatings, the polymer swells and binds with moisture. The moisture may then be released to the environment. It thereby provides an enhanced evaporative cooling effect that exceeds other technologies. These coatings are therefore highly attractive to the performance fabric markets, including protective clothing, active outerwear, bedding, military and intimate apparel.
However, there is a growing demand that such coatings (a) can be applied solvent-free (which refers to organic solvents mentioned above), and (b) survive multiple laundering cycles without visual loss of coating and/or loss of performance.
The inventors set out to solve this problem.